MOLECULAR-STRUCTURE OF RARE BUT GEOGRAPHICALLY WIDESPREAD SN-GLYCEROL-3-PHOSPHATE DEHYDROGENASE ULTRA-FAST ELECTROPHORETIC ALLELES IN DROSOPHILA-MELANOGASTER

Six naturally occurring but rare alleles of sn-glycerol-3-phosphate de hydrogenase (Gpdh) in Drosophila melanogaster have been investigated i n this study. They all belong to a class of Gpdh(UF) (ultra-fast) alle les, because their electrophoretic mobilities are faster than that of the Gpdh(F) (fast) allele. The Gpdh(UF) variants are widespread, and h ave been reported from five continents. DNA sequence analysis has show n that the change in electrophoretic mobility was in each allele cause d by a single amino acid residue substitution in the encoded protein. In the Xiamen(UF) allele it is a substitution of lysine (AAA) to aspar agine (AAT) in exon 1 (residue 3). An asparagine (AAT) to aspartate (G AT) change was found in exon 6 (residue 336) in the Iowa(UF) and Nethe rlands(UF) alleles. The mobility of the Raleigh(UF) allele was altered by a valine (GTG) to glutamate (GAG) substitution in exon 3 (residue 76). Two mutations were detected in the Brazzaville(UF) allele: a lysi ne (AAG) to methionine (ATG) substitution in exon 2 (residue 68) is re sponsible for the ultra-fast phenotype of this variant, while a tyrosi ne (TAT) to phenylalanine (TTT) substitution in exon 4 (residue 244) i s not expected to alter the electrophoretic mobility of the encoded pr otein. These results indicate that the Gpdh(UF) alleles originate from different mutational events, and only two of them - Iowa(UF) and Neth erlands(UF) - might share a common ancestry. The GPDH activity of the Iowa(UF) allele is intermediate between those of the Gpdh(S) and Gpdh( F) control stocks. The other Gpdh(UF) variants have lower activities t han the controls: Xiamen(UF) - 83%, Raleigh(UF) - 80% and Brazzaville( UF) - 73% of the Gpdh(F) control.